(a) Field of the Invention
The present invention relates to a polyvalent metal salt of a salicylic acid resin useful as a developer for a recording material for use in pressure sensitive recording material and the like, and a process for preparing the polyvalent metal salt of the resin. In addition, it relates to an aqueous dispersion in which the polyvalent metal salt of the salicylic acid resin is dispersed, and a developing sheet in which the polyvalent metal salt of the resin is used.
(b) Description of the Prior Art
It is known that metal salts of salicylic acid derivatives are useful as developers for pressure sensitive recording materials, and methods for preparing and utilizing various salicylic acid derivatives and their metal salts have been heretofore disclosed.
1. A 3,5-disubstituted salicylic acid derivative has been prepared from a corresponding 2,4-disubstituted phenol derivative and carbon dioxide by the utilization of the so-called Kolbe-Schmitt reaction (Japanese Patent Publication No. 25174/1976 and U.S. Pat. No. 3,983,292).
In this method, however, two steps are required to manufacture the 3,5-disubstituted salicylic acid derivative from phenol, and for the reaction of carbon dioxide, a specific high-temperature high-pressure device is necessary and so the inconvenience of facilities for the manufacture is present. Furthermore, when a metal salt of the 3,5-disubstituted salicylic acid derivative, for example, zinc salt of 3,5-di(.alpha.-methylbenzyl)salicylic acid is used as a developer for pressure sensitive recording material, there is a problem that a colored image disappears with water.
2. Another method is known in which 1 mol of salicylic acid is reacted with at least 2 mols of a phenyl ethanol derivative to produce 4-[.alpha.-methylbenzyl(.alpha.-methylbenzyl)]salicylic acid derivative (Japanese Patent Publication No. 61110/1993 and U.S. Pat. No. 4,754,063).
3. Methods for preparing a polyvalent metal salt of 3,5-di(.alpha.-methylbenzyl)salicylic acid derivative and a polyvalent metal salt of 4-[.alpha.-methylbenzyl(.alpha.-methylbenzyl)]salicylic acid derivative are disclosed in which 1 mol of salicylic acid is reacted with at least 2 mols of a styrene derivative in the presence of an aromatic sulfonic acid, and the resulting reaction product is then reacted with a polyvalent metal salt of an inorganic acid or a lower aliphatic carboxylic acid (Japanese Patent Publication No. 75736/1993 and U.S. Pat. No. 4,748,259).
When the polyvalent metal salt (e.g., a zinc salt) of 4-[.alpha.-methylbenzyl(.alpha.-methylbenzyl)]salicylic acid prepared by these methods is used as a developer for pressure sensitive recording material, the resulting colored image is poor in storage stability, and for example, if brought into contact with water, the colored image disappears inconveniently.
4. Still another method is disclosed in which salicylic acid is reacted with a styrene compound in the presence of an aliphatic carboxylic acid by the use of an organic sulfonic acid or an inorganic acid as a catalyst to produce a 3,5-di(.alpha.-methylbenzyl)salicylic acid derivative (Japanese Patent Application Laid-open No. 91043/1990).
When a polyvalent metal salt (e.g., a zinc salt) of 3,5-di(.alpha.-methylbenzyl)salicylic acid prepared by these methods is used as a developer for pressure sensitive recording material, the resulting colored image is poor in storage stability, and for example, if brought into contact with water, the colored image disappears inconveniently, as in the above case.
5. There is disclosed a further method in which a salicylic acid derivative is reacted with a styrene derivative at 40.degree. to 170.degree. C. in the presence of an acid catalyst, and the resulting reaction product is then reacted with a metal salt of a fatty acid to form a metal salt of a polymeric salicylic acid resin (Japanese Patent Application Laid-open No. 112537/1988 and U.S. Pat. No. 4,929,710). However, the metal salt of the salicylic acid resin formed by this method is often colored disadvantageously. Moreover, when the metal salt (e.g., a zinc salt) of the polymeric salicylic acid resin formed by this method is used as a developer for pressure sensitive recording material, it is difficult to bring the zinc salt into fine particles at the time of dispersion, and the resulting dispersion is liable to coagulate inconveniently. In addition, a developing sheet for pressure sensitive recording material which can be prepared by the use of the resulted polyvalent metal salt of the salicylic acid resin has a drawback such as poor abrasion resistance, which is not preferable as the developer for the pressure sensitive recording materials.
6. Furthermore, a method for manufacturing a polyvalent metal salt of a salicylic acid resin is disclosed which comprises reacting a salicylic acid ester with a styrene, hydrolyzing the resultant salicylic acid ester resin, and then reacting a polyvalent metal compound with the hydrolyzed resin (Japanese Patent Application Laid-open No. 133780/1989 and U.S. Pat. No. 4,952,648). For example, there is described a method which comprises reacting methyl salicylate with styrene in the presence of concentrated sulfuric acid to form a methyl salicylate resin, hydrolyzing this resin with an aqueous alkaline solution, and then reacting the hydrolyzed resin with a polyvalent metal compound (e.g., zinc sulfate) to produce the polyvalent metal salt of the salicylic acid resin. However, when used as a developer for pressure sensitive recording material, the polyvalent metal salt (e.g., zinc salt) of the salicylic acid resin obtained by this method is scarcely brought into fine particles at the time of dispersion, and the resultant dispersion is liable to coagulate inconveniently.
As described above, the performance of the product obtained by the reaction between a salicylic acid derivative and a styrene derivative and the polyvalent metal salt of this product depends upon the given reaction conditions (e.g., catalyst, solvent, reaction temperature and the like). Therefore, physical properties of the product and the polyvalent metal salt of the product cannot be determined in a theoretical manner, and it is also very difficult to presume them on the basis of experience. Nowadays, it is expected that the above performance and physical properties are elucidated and established by experimental procedures.
In recent years, there is desired a developer which can easily be prepared as fine particles and which is excellent in storage stability as a dispersion, is excellent in storage stability (e.g., water resistance) as a colored image in the case that a developing sheet for pressure sensitive recording material is formed therefrom, and is excellent in abrasion resistance stability.